Ni-base alloy

Abstract

In a Ni-base alloy, an area-equivalent diameter D is calculated. D is defined by D=A 1/2 from an area A of a largest nitride in a field of view when an observation area S 0 is observed. This process is repeated in n fields of view for measurement, where n is the number of the fields of view for measurement, so as to acquire n pieces of data on D, and the pieces are arranged in ascending order D 1 , D 2 , . . . , D n to obtain a reduced variate y j . The obtained values are plotted on X-Y axis coordinates, where an X axis corresponds to D and a Y axis corresponds to y j . In a regression line y j =a×D+b, y j is obtained when a target cross-sectional area S is set to 100 mm 2 . When the obtained y j is substituted into the regression line, the estimated nitride maximum size is ≦25 μm in diameter.

The invention claimed is: 
     
       1. A cast and plastically-worked Ni-base alloy comprising:
 13 mass % to 30 mass % of Cr; 
 0.01 mass % to 6 mass % of Ti; 
 8 mass % or less of Al; and 
 25 mass % or less of Fe, wherein 
 nitrides are present, and 
 an area-equivalent diameter D is calculated, and the area-equivalent diameter D is defined by D=A 1/2  from an area A of a largest nitride in a field of view when observation is performed at a magnification of 400 times to 3000 times for an observation area S 0  for measurement, this process is repeated in n fields of view for measurement, where n is the number of the fields of view for measurement, so as to acquire n pieces of data on the area-equivalent diameter D, and the pieces of data on the area-equivalent diameter D are arranged in ascending order of D 1 , D 2 , . . . , D n  to obtain a reduced variate y j  which is defined by the following Expression (1):
   [Formula 1] 
     y   j =−ln [−ln { j /( n+ 1)}]  (1)
 
 
 (in the Expression (1), j is a rank number when the pieces of data on the area-equivalent diameter D are arranged in ascending order), 
 the obtained values are plotted on X-Y axis coordinates, where an X axis corresponds to the area-equivalent diameter D and a Y axis corresponds to the reduced variate y j , a regression line y j =a×D+b (a and b are constants) is obtained, and when a target cross-sectional area S for prediction is set to 100 mm 2 , y j  is obtained through the following Expression (2): 
 
       
         
           
             
               
                 
                   
                     [ 
                     
                       Formula 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     ] 
                   
                 
                 
                   
                       
                   
                 
               
               
                 
                   
                     
                       
                         y 
                         j 
                       
                       = 
                       
                         - 
                         
                           ln 
                           ⁡ 
                           
                             ( 
                             
                               
                                 - 
                                 ln 
                               
                               ⁢ 
                               
                                 S 
                                 
                                   
                                     S 
                                     0 
                                   
                                   + 
                                   S 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                     , 
                   
                 
                 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
          and 
         when the obtained value of y j  is substituted into the regression line to calculate an estimated nitride maximum size, the estimated nitride maximum size is equal to or less than 25 μm in terms of area-equivalent diameter. 
       
     
     
       2. The cast and plastically-worked Ni-base alloy according to  claim 1 , wherein the nitride is a titanium nitride.